A bi-fold door is a type of sliding door that has multiple hinged sections that fold together as the door is opened, and thus it is conventionally locked by way of vertical shoot bolts that project from the door into the surrounding frame so as to anchor the door at its top and bottom. The shoot bolts are typically connected by rods to shoot bolt arms of a central lock, and the shoot bolt arms are operatively coupled to a rotating driver so as to be moved linearly in opposite directions as the driver rotates. The rotating driver is typically provided as a follower to the spindle of a lever style handle, and thus when the handle is in one orientation (e.g. horizontal) the shoot bolts are fully retracted and when the handle is in another orientation (e.g. vertical) the shoot bolts are fully extended.
In the bi-fold door lock marketed by Assa Abloy Australia Pty Limited (Sherwood QLD) as the TWIN BOLT LOCK, the spindle follower is rotatably mounted in one side of the lock casing and a tensioning disk is mounted at the other end of the spindle follower. The tensioning disk has four flattened sections that interact with the flat interior side walls of the lock casing to bias the follower towards two different home positions corresponding to the shoot bolts being either fully extended or fully retracted. The rotation of the spindle follower is converted to opposite linear motion of the shoot bolt arms by way of a planetary gear system, i.e. the spindle follower is the central gear and each shoot bolt arm is pivotably linked to a respective satellite gear. And for applications requiring additional security, deadlocking is provided by using a key cylinder to press a locking plate into engagement with the follower, thereby preventing the follower from rotating.
While a bi-fold style lock can generally be employed in other types of doors, such as in the secondary door of a set of French doors, there are unique challenges to meeting the demands of bi-fold doors. This is because in most bi-fold doors applications, it is desirable to have the handle mounted on only one side of the door (the interior side) in order to leave the other side (the exterior side) unobstructed. This allows the sections to lay flat against each other when the door is fully opened, but it also results in the exterior end of the spindle being unsupported. Thus, as one pulls on the lever handle to open a bi-fold door, there can be a tendency for the spindle to move or shift within the lock.
As present bi-fold lock designs suffer from a variety of drawbacks, limitations, disadvantages and problems, there is need for improvement in the art.